Conventionally, generally, a catalyst of a heterogeneous system and a catalyst of a homogeneous system are known as a catalyst for hydrogenation to be used in the step of hydrogenating an olefinic compound.
Although the catalyst of the heterogeneous system generally is industrially widely used, the catalyst of the heterogeneous system have lower activity than that of the latter catalyst of the homogeneous system and have the problem of being economically inefficient, because the catalysts of the heterogeneous system is required to be used at a large amount for a desired hydrogenation reaction, and the reaction is at a high temperature and a high pressure.
On the other hand, since a hydrogenation reaction using the catalyst of the homogeneous system generally proceeds in a homogeneous system, there are features that the catalyst of the homogeneous system have a higher activity, require a lower amount of used catalyst, and are capable of hydrogenation at a lower temperature and a lower pressure than the catalyst of the heterogeneous system. However, the catalyst of the homogeneous system have the drawbacks that the catalysts preparation is complex, the stability of the catalyst itself is low, reproducibilities are poor, and side reactions tend to occur. Moreover, the catalyst of the homogeneous system also have the problem that sufficient activity of hydrogenation is not obtained when hydrogenating a alkyl-substituted olefinic unsaturated double bond having a steric hindrance.
Accordingly, there is currently a strong need for the development of a catalyst of hydrogenation which has a high activity and which can be handled easily.
On the other hand, for a polymer containing an olefinic unsaturated double bond, although the unsaturated double bond is advantageously utilized in vulcanization and the like, due to this double bond, the polymer also has drawbacks regarding poor stability, such as heat resistance and oxidation resistance. Such the drawback regarding poor stability is substantially improved by hydrogenating the polymer to remove the unsaturated double bonds in the polymer chain.
However, when hydrogenating the polymer, as compared with hydrogenating a low-molecular-weight compound, the polymer is more easily affected by the viscosity of the reaction system, steric hindrance of the polymer chain and the like, which makes hydrogenation more difficult. In addition, there is a problem that it is difficult to physically remove all the catalyst, after hydrogenation has finished. Therefore, there is a problem of causing filter clogging to an extruder used upon the production of a hydrogenated unsaturated double bond-containing compound.
As described above, there has long been an issue for obtaining a catalyst composition for hydrogenation that is economically efficient not to need to be used in a large amount, has a high storage stability, can exhibit sufficient activity of hydrogenation even when hydrogenating olefinic unsaturated double bonds having a steric hindrance, and has a low degree of filter clogging in an extruder upon the production of a hydrogenated unsaturated double bond-containing compound.
Patent Literatures 1 and 2 disclose a method of hydrogenating an olefinic compound using a combination of a specific titanocene compound and an alkyllithium; Patent Literatures 3 and 4 disclose a method of hydrogenating an olefinic unsaturated (co)polymer using a combination of a metallocene compound, with organic aluminum, organic zinc, organic magnesium and the like; and Patent Literatures 5 and 6 disclose a method of hydrogenating an olefinic unsaturated group-containing living polymer using a combination of a specific titanocene compound and an alkyllithium.
Moreover, Patent Literature 7 discloses a method of hydrogenating an olefinic double bond in an olefinic unsaturated double bond-containing polymer using a combination of a specific titanocene compound and an alkoxylithium. This method requires an expensive organic metal compound other than alkoxylithium as a reductant.
Furthermore, Patent Literature 8 discloses a method of hydrogenating an olefinic unsaturated double bond-containing polymer using a combination of a specific titanocene compound, an olefin compound, and a reductant.
Further, Patent Literature 9 discloses a method of hydrogenating an olefin compound using a combination of a metallocene compound having a pentamethylcyclopentadienyl group, which is formed by substituting all of five hydrogens of a cyclopentadienyl group with methyl groups, and a reductant.
Still further, Patent Literatures 10 and 11 disclose a method of hydrogenating an olefin compound using a catalyst composition for hydrogenation comprising a specific titanocene compound, a reductant, an olefinic unsaturated double bond-containing polymer, and a polar compound.
Still further, Patent Literature 12 discloses a method of hydrogenating an olefin compound using a catalyst composition for hydrogenation comprising a specific metallocene compound and a compound selected from a conjugated diene monomer, an acetylenic compound and an acetylenic monomer.